This invention relates to an ultrasonic obstacle sensor for use with an automotive vehicle. More particularly, it relates to an ultrasonic obstacle sensor for an automotive vehicle with an adjustable suspension which can adjust the hardness of the vehicle suspension when an obstacle, such as an object lying on a road or a pothole in the road surface, is detected so as to lessen the shock imparted by the obstacle to the passengers of the vehicle.
Various type of ultrasonic obstacle sensors for automobiles have been proposed in the past. For example, Japanese Published Examined Patent Application 1-30436 (1989) discloses a sensor for sensing obstacles around the body of a vehicle. Ultrasonic waves are transmitted to around the vehicle body, and based on the presence or absence of waves reflected back to the vehicle, it is determined whether an obstacle is present. In order to prevent reflected waves from a normal road surface on which the vehicle is travelling from being incorrectly sensed as reflected waves from obstacles, it is necessary either to increase the directionality of the ultrasonic receiver for receiving the reflected waves, or to transmit the ultrasonic waves substantially horizontally so that no waves will be reflected from the road surface. As a result, however, the reflected waves are not received well by the sensor, so accurate obstacle detection can not be performed.
Japanese Published Unexamined Patent Application No. 62-131813 discloses an ultrasonic sensor for sensing the road surface condition in front of a moving vehicle. In that application, an ultrasonic transmitter is mounted on a vehicle so as to continuously transmit ultrasonic waves diagonally forwards towards the road surface. However, the device of that application suffers from the following problems:
(1) Since the ultrasonic transmitter transmits continuously, the amount of heat generated by the transmitter can become very large. In order to prevent overheating, the ultrasonic wave energy must be suppressed to a low level, with the result that the waves reflected from the road surface are weak and difficult to detect.
(2) Due to the continuous transmission by the ultrasonic transmitter, interference occurs between the transmitted waves and the reflected waves, making it difficult to detect the reflected waves. Standing waves are also a problem. As a result, accurate obstacle detection can not be performed.
(3) Reflected waves from the road surface can not be differentiated from other reflected waves.
(4) Variation in the strength of reflected waves due to causes such as wind or temperature irregularities can not be distinguished from variation due to road surface irregularities.
Thus, at present, there is no device which can accurately detect obstacles such as potholes, rocks, and the like in or on the surface of a road on which a vehicle is travelling.